Question 732083
Let {{{ x }}} = last month's sales
{{{ .04x = 7200 }}}
{{{ x = 7200/.04 }}}
{{{ x = 180000 }}}
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He wants to earn $8,000 in commission this month. 
Let {{{ y }}} = increase in sales over last month's sales
{{{ .04*( 180000 + y )  = 8000 }}}
{{{ 7200 + .04y = 8000 }}}
{{{ .04y = 800 }}}
{{{ y = 800 / .04 }}}
{{{ y = 20000 }}}
He must  increase his sales by $20,000 over last month's sales